A consist includes one or more locomotives that are coupled together to produce motive power for a train of rail vehicles. The locomotives each include one or more engines, which combust fuel to produce mechanical power. The engine(s) of each locomotive can be supplied with liquid fuel (e.g., diesel fuel) from an onboard tank, gaseous fuel (e.g., natural gas) from a tender car, or a blend of the liquid and gaseous fuels. The mechanical power produced by the combustion process is directed through a generator and used to generate electricity. The electricity is then routed to traction motors of the locomotives, thereby generating torque that propels the train. The locomotives can be connected together at the front of the train or separated and located at different positions along the train. For example, the consist can be positioned at the front, middle, or end of the train. In some instances, more than one consist can be included within a single train. In some consists, the locomotives include computer systems for maintaining operations of the locomotive.
Because the locomotives of a consist must cooperate to propel the train, communication between the locomotives can be important. Historically, this communication has been facilitated through the use of an MU (Multi-Unit) cable that extends along the length of the consist. An MU cable is comprised of many different wires, each capable of carrying a discrete signal used to regulate a different aspect of consist operation. For example, a lead locomotive generates current within a particular one of the wires to indicate a power level setting requested by the train operator. When this wire is energized, the engines of all trailing locomotives are caused to operate at a specific throttle value. In another example, when one locomotive experiences a fault condition, another of the wires is energized to alert the other locomotives of the condition's existence.
In some consists, locomotives communicate via their respective computer systems on an Ethernet network formed over the MU cables, or other intra-consist electrical cables. With this configuration, network data can be transmitted from the computer system in the lead locomotive to the computer systems in the trail locomotives, and vice-versa. The network data includes data that is packaged as data packets and uniquely addressed to particular computer systems, or portions of the computer systems. The network data can be, for example, vehicle sensor data indicative of vehicle health, commodity condition data, temperature data, weight data, and security data. The network data is transmitted orthogonal to conventional non-network (i.e., command) data that is already being transmitted on the MU cable.
Traditionally, communication over a MU cable or other intra-locomotive cable was limited to voltage levels for individual wires within the MU cable. For example, a high voltage applied to an individual wire might indicate one value, while a low or zero voltage applied to the individual wire might indicate a second value. While MU cables provide an existing infrastructure that can be used by the computer systems of locomotives to communicate network data, MU cables were not designed for network data communication. For example, the wires within a MU cable are not shielded or twisted and are subject to interference. As a result, signal strength can degrade significantly as the signal propagates the length of a MU cable. For example, in a locomotive consist, the locomotive computer system adjacent to the signal's origin might receive the signal at 10 dBm, a locomotive further away in the consist might receive the signal at −30 dBm, which may be too weak to effectively transmit network data.
The signal degradation can be overcome by increasing strength of the signal when it is transmitted. While increasing the transmit signal allows for adequate signal strength to reach locomotive computer systems far away from the origin of the signal, it can overload the components of locomotive computer systems that are located close to the origin of the signal. For example, increasing the signal strength might produce a received 10 dBm signal at a locomotive further away from the origin of the signal, but might overload a locomotive computer system close to the origin of the signal with a 20 dBm signal.
Thus, one solution for overcoming signal degradation is to increase the strength of the transmit signal, but attenuate the signal on the receive end so as to not overload computer systems receiving the signal. Such a solution is described in U.S. Patent Publication No. 2012/0163201 (the '201 publication) filed by Williams et al. and published on Jun. 28, 2012. The '201 publication describes a cable modem auto-attenuation system capable of taking a high-power signal from the cable plant's service line, dropping the power value down to a usable level and transmitting the signal to a cable modem. Although the system of the '201 publication may minimally solve the problem of overcoming signal degradation over cable, the system would not be adequate for a train communication network because it is not adapted to interface with train communication hardware and does not provide the granularity of attenuation control needed for train communication networks.
The disclosed communication network is directed to overcoming one or more of the problems set forth above.